Five current US Senators have previously held statewide office as Secretary of State, but none of them were directly elected to the Senate from that job. Three served in the US House in between (Roy Blunt, Dean Heller, Sherrod Brown), while two went from SoS to Senator via serving as Governor of West Virginia (Jay Rockefeller, Joe Manchin).
State Attorneys General have more success, with eight currently serving in the Senate. Five went straight from Attorney General to Senator (Cornyn, Sessions, Pryor, Blumenthal, Ayotte) while two former Attorneys General left public office and were later elected to the Senate (Heitkamp, Whitehouse). One former AG served in the US House before the Senate (Tom Udall).
As for other statewide offices:
Bob Casey Jr. was Pennsylvania's State Treasurer when elected to the Senate, and had previously served as the state's Auditor General, but he's a special case- he had high name recognition from a failed Gubernatorial bid two years prior, and his father was a former governor.
Claire McCaskill was elected to the Senate while serving as MO State Auditor, but was well known in the state because she had lost a very close gubernatorial election just two years before her Senate run.
Bill Nelson was elected to the Senate while serving as Florida Treasurer, but he had previously served in the US House and only resigned from there in a failed attempt to run for Governor.
Mazie Hirono was once Lt. Governor of Hawaii but served in the US House after a failed gubernatorial bid.
Brian Shatz was serving as Lt. Governor of Hawaii when he was appointed to the Senate.
John Walsh had served as Montana's Adjutant General and was elected Lt. Governor before he was appointed to the Senate.
Risch and Kaine were Lt. Governors who got promoted to Governor before running for the Senate.
Harry Reid was NV Lt. Gov but was in the US House before being elected to the Senate.
Based on all the above, here are some basic guidelines about downballot statewide officeholders running for the Senate:
- Incumbent State Attorneys General actually have a realistic shot of winning a Senate election.
- For any other downballot officeholder, they will probably only be elected to the Senate if they have previously ran for Governor (I assume the campaign experience, increased name recognition, and leftover campaign infrastructure all help here).
- If one of these officeholders wants to be in the Senate they are better off angling for an appointment to fill a vacancy than trying to win an open election.
- They have more chance if they run for Governor or Congress first, because those are the most common springboards into the Senate.
tl;dr: the typical progression is State Office to U.S. House or Governor, and then to U.S. Senate. People who skip the middle step will only be successful if they have already tried to run for Governor but failed, if they get appointed, or if they are an Attorney General.
